public override IEnumerable <string> SampleMatches(int k, int randomseed)
{
// Zero is treated as no seed, instead using a system provided one
Random random = randomseed != 0 ? new Random(randomseed) : new Random();
ISolver <TSet> solver = _builder._solver;
CharSetSolver charSetSolver = _builder._charSetSolver;
// Create helper BDDs for handling anchors and preferentially generating ASCII inputs
BDD asciiWordCharacters = charSetSolver.Or(new BDD[] {
charSetSolver.CreateBDDFromRange('A', 'Z'),
charSetSolver.CreateBDDFromRange('a', 'z'),
charSetSolver.CreateBDDFromChar('_'),
charSetSolver.CreateBDDFromRange('0', '9')
});
// Visible ASCII range for input character generation
BDD ascii = charSetSolver.CreateBDDFromRange('\x20', '\x7E');
BDD asciiNonWordCharacters = charSetSolver.And(ascii, charSetSolver.Not(asciiWordCharacters));
// Set up two sets of minterms, one with the additional special minterm for the last end-of-line
Debug.Assert(_builder._minterms is not null);
int[] mintermIdsWithoutZ = new int[_builder._minterms.Length];
int[] mintermIdsWithZ = new int[_builder._minterms.Length + 1];
for (int i = 0; i < _builder._minterms.Length; ++i)
{
mintermIdsWithoutZ[i] = i;
mintermIdsWithZ[i] = i;
}
mintermIdsWithZ[_builder._minterms.Length] = _builder._minterms.Length;
for (int i = 0; i < k; i++)
{
// Holds the generated input so far
StringBuilder inputSoFar = new();
StringBuilder?latestCandidate = null;
// Current set of states reached initially contains just the root
NfaMatchingState states = new(_builder);
// Here one could also consider previous characters for example for \b, \B, and ^ anchors
// and initialize inputSoFar accordingly
states.InitializeFrom(_initialStates[GetCharKind(ReadOnlySpan <char> .Empty, -1)]);
CurrentState statesWrapper = new(states);
// Used for end suffixes
List <string> possibleEndings = new();
while (true)
{
Debug.Assert(states.NfaStateSet.Count > 0);
// Gather the possible endings for satisfying nullability
possibleEndings.Clear();
if (NfaStateHandler.CanBeNullable(ref statesWrapper))
{
// Unconditionally final state or end of the input due to \Z anchor for example
if (NfaStateHandler.IsNullable(ref statesWrapper) ||
NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.BeginningEnd))
{
possibleEndings.Add("");
}
// End of line due to end-of-line anchor
if (NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.Newline))
{
possibleEndings.Add("\n");
}
// Related to wordborder due to \b or \B
if (NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.WordLetter))
{
possibleEndings.Add(ChooseChar(random, asciiWordCharacters, ascii, charSetSolver).ToString());
}
// Related to wordborder due to \b or \B
if (NfaStateHandler.IsNullableFor(_builder, ref statesWrapper, CharKind.General))
{
possibleEndings.Add(ChooseChar(random, asciiNonWordCharacters, ascii, charSetSolver).ToString());
}
}
// If we have a possible ending, then store a candidate input
if (possibleEndings.Count > 0)
{
latestCandidate ??= new();
latestCandidate.Clear();
latestCandidate.Append(inputSoFar);
//Choose some suffix that allows some anchor (if any) to be nullable
latestCandidate.Append(Choose(random, possibleEndings));
// Choose to stop here based on a coin-toss
if (FlipBiasedCoin(random, SampleMatchesStoppingProbability))
{
yield return(latestCandidate.ToString());
break;
}
}
// Shuffle the minterms, including the last end-of-line marker if appropriate
int[] mintermIds = NfaStateHandler.StartsWithLineAnchor(_builder, ref statesWrapper) ?
Shuffle(random, mintermIdsWithZ) :
Shuffle(random, mintermIdsWithoutZ);
foreach (int mintermId in mintermIds)
{
bool success = NfaStateHandler.TakeTransition(_builder, ref statesWrapper, mintermId);
Debug.Assert(success);
if (states.NfaStateSet.Count > 0)
{
TSet minterm = _builder.GetMinterm(mintermId);
// Append a random member of the minterm
inputSoFar.Append(ChooseChar(random, ToBDD(minterm, solver, charSetSolver), ascii, charSetSolver));
break;
}
else
{
// The transition was a dead end, undo and continue to try another minterm
NfaStateHandler.UndoTransition(ref statesWrapper);
}
}
// In the case that there are no next states or input has become too large: stop here
if (states.NfaStateSet.Count == 0 || inputSoFar.Length > SampleMatchesMaxInputLength)
{
// Ending up here without an ending is unlikely but possible for example for infeasible patterns
// such as @"no\bway" or due to poor choice of c -- no anchor is enabled -- so this is a deadend.
if (latestCandidate != null)
{
yield return(latestCandidate.ToString());
}
break;
}
}
}
/// <summary>
/// Gets a <see cref="BDD"/> that represents <see cref="WordLetter"/> together with the characters
/// \u200C (zero width non joiner) and \u200D (zero width joiner) that are treated as if they were
/// word characters in the context of the anchors \b and \B.
/// </summary>
public static BDD WordLetterForAnchors(CharSetSolver solver) =>
s_wordLetterForAnchors ??
Interlocked.CompareExchange(ref s_wordLetterForAnchors, solver.Or(WordLetter(solver), solver.CreateBDDFromRange('\u200C', '\u200D')), null) ??
s_wordLetterForAnchors;